1. Technical Field
The present invention relates to a piezoelectric device including a piezoelectric resonator element such as quartz stored in a package, in particular, a supporting unit for the piezoelectric resonator element.
2. Related Art
A piezoelectric device such as a quartz resonator including a quartz resonator as a piezoelectric resonator element is widely used for mobile phones and IC cards (See JP-A-2004-35781 and 2004-297198, for examples.) FIG. 11 shows a conventional piezoelectric device for explanation. FIG. 11 is a perspective view of a structure of a conventional piezoelectric element. As shown in the figure, a quartz resonator 121 as an example of the conventional piezoelectric device comprises a connecting electrode 127 formed on a base substrate 123 and a quartz resonator element 122 connected to the electrode via a conductive adhesive 128. The quartz resonator element 122 comprises a pair of oscillating arms 130, a pair of supporting arms 126 and a base 124 connecting oscillating arms 130 and supporting arms 126, which are integrally formed. Oscillating arms 130 having almost the same configuration are extended in parallel with each other from the end of the base 124. A groove 131 is formed both on the front and back surfaces of oscillating arms 130 to improve an oscillating property (see JP-A-2002-261575 for example.) Further, an end weight layer 125 for arranging a frequency is formed both on the front and back surfaces of oscillating arms 130. A connecting electrode 127 is formed on a base substrate 123 to have a step against the upper surface of the base substrate 123 and supporting arms 126 are located on the connecting electrode 127 and connected via the conductive adhesive 128. This connection yields a space between the upper surface of the base substrate 123 and the quartz resonator 122.
In the quartz resonator element 122, an adhesive material that is under high viscosity is coated on the connecting electrode 127. Supporting arms 126 are placed on the adhesive material and connected to the connecting electrode 127 by hardening of the adhesive material. Here, when the quartz resonator element having the conventional size (the length 2400 μm, the width 500 μm and the thickness 100 μm) is connected, the central gravity of the quartz resonator element 122 of which a part is located on the conductive adhesive 128 is sunk with respect to the length of oscillating arms 130. As a result of it, the base side or the end side of the quartz resonator element 122 is near to the base substrate 123. In order to avoid this accession, the joint positions of supporting arms 126 are set around the central gravity of the quartz resonator element 122 with respect to the length direction of the oscillating arms 130, for example (see JP-A-2004-2971798.)
The conventional quartz element 121, however, has a disadvantage in that the quartz resonator element 122 is deformed while supporting arms 126 work as a fulcrum, when excessive shock such as falling down is applied to the vertical direction of the element 121, making the edge of the end weight layer 125, which is the most far from the fulcrum, collide with the upper surface of the base substrate 123. This collision damages or deforms oscillating arms 130 due to the weakness of the end weight layer 125 against such shock, deteriorating an oscillating characteristic such as the mismatching of the CI value or a resonant oscillation frequency.